Power cut off mode for conserving power in electronic devices

ABSTRACT

External jolts, such as those occurring during shipment, may inadvertently activate an electronic device. Such inadvertent activations may result in the electronic device entering an active mode during shipment, draining battery power. This document describes a power cut off mode that prevents inadvertent device activations and minimizes current consumption during shipment or storage of a device. This conserves battery power for operational use by the user.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of, and claims priority to, U.S.patent application Ser. No. 12/770,031, filed Apr. 29, 2010, issued asU.S. Pat. No. 8,635,481, and which is incorporated by reference hereinin its entirety.

BACKGROUND

Electronic devices, such as electronic book readers (“eBook readerdevices”), cellular telephones, portable media players, desktopcomputers, laptops, tablet computers, netbooks, personal digitalassistants, and the like, rely on electrical power to function.

Within these electronic devices, several components utilize significantamounts of power during operation, including the processor(s) andperipheral devices. These peripheral devices include external memoryinterfaces (EMIs), Universal Serial Bus (USB) controllers, imageprocessing units (IPUs), and so forth. These peripheral devices mayreside on the same “chip” or die as the processor and/or may reside onanother die.

Inadvertent activation of the electronic device due to environmentalfactors may occur. For instance, devices may experience transientaccelerations from jostling during transport and, in response, mayactivate or power up certain components of the device. For example, abox containing the electronic device may be dropped during shipment.Such a drop may inadvertently activate the device. During inadvertentactivation, the electronic device consumes power, thus depleting poweravailable in a battery powering the electronic device. A user that laterattempts to use the electronic device may thus find the batterysubstantially or completely discharged. The user is therefore requiredto charge the device, a process which may be inconvenient and takeseveral hours, depending upon the charger, battery capacity, and otherparameters.

While mechanical switches with high activation forces may mitigate thisproblem, these solutions introduce other problems. For instance, designand engineering constraints, such as available volume, ability tocontrol the device, and so forth, may preclude device designers fromincluding such mechanical switches in electronic devices. Furthermore,such an approach may render inoperable a real-time clock of the device,introducing adverse side effects with regard to digital rightsmanagement (DRM).

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is set forth with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different figures indicates similaror identical items.

FIG. 1 is an illustrative electronic device (here, an eBook readerdevice) configured with a power cut off module for placing the eBookreader device into a power cut off mode, thereby reducing inadvertentactivations and conserving battery power.

FIG. 2 is an illustrative schematic of the eBook reader deviceconfigured to use the power cut off module of FIG. 1.

FIG. 3 is an illustrative process of the power cut off module preventinginadvertent activation.

FIG. 4 is an illustrative flow diagram of a process for awakening adevice from sleep mode and entering a power cut off mode.

FIG. 5 is an illustrative flow diagram of a process for engaging a powercut off mode.

FIG. 6 is an illustrative flow diagram of a process for restarting adevice in the power cut off mode.

DETAILED DESCRIPTION Overview

As described above, inadvertent activation of electronic devicesdepletes power stored in a battery. This creates inconvenience byrequiring a user to locate and employ an external power supply, spendtime charging the battery, or replace the battery before actuallyoperating the device.

Traditional “off modes” may maintain a power management integratedcircuit in an active state, resulting in significant consumption ofpower. Over time, such as during shipment or storage, this consumptionmay deplete the battery. Also, traditional off modes may deactivate thereal-time clock, complicating digital rights management (DRM) or otherfunctions. Furthermore, traditional off modes may be susceptible toawakening as a result of transient wakeup interrupts, resulting in evenmore rapid discharge and depletion of the battery.

This disclosure describes techniques for placing a device into a powercut off mode. While in the power cut off mode, a sustained wakeupinterrupt will awaken the device, while transient wakeup interrupts willnot. Also, while the device is in the power cut off mode describedherein the power management integrated circuit maintains a real-timeclock and minimal circuitry configured to accept a sustained wakeupinterrupt. As a result, a large portion of the power managementintegrated circuit remains off, which significantly reduces powerconsumption. Such significant reductions in power consumption minimizebattery depletion, thus extending the shelf life of the electronicdevice. In addition, the operational real-time clock facilitatesdate/time related functions such as DRM.

The techniques described herein may apply to electronic devices and mayprovide the ability to access content via a network connection. Forexample, an eBook reader device may have a wireless network connectionto allow convenient access to content stored elsewhere and accessible bythe network connection. The content accessed on the device may besubject to DRM restraints. In several implementations of DRM, real-timedate and time are at least one of the inputs used to determineaccessibility.

For example, DRM may call for an electronic book to be accessible foronly a specific two month period, such as when loaned from a library.During the period, the electronic book is accessible, while at theexpiration of the period the electronic book is inaccessible. Withoutthe real-time clock, or access to an external authoritative time server,DRM may be inoperable, precluding access to content that the user may beentitled to.

When in the power cut off mode, a sustained wakeup interrupt will awakenthe device. The sustained wakeup interrupt includes, for example, theinterrupt generated by a user intentionally activating a power switch orfrom attachment of a charger. The power cut off mode protects the devicefrom inadvertent activations, such as from brief contacts of a powerswitch due to transient accelerations, because the power managementintegrated circuit in power cut off mode requires a sustained wakeupinterrupt to activate.

In some implementations, the device may enter the power cut off modeafter meeting one or more pre-determined conditions. For example, thepre-determined condition may be an elapsed time limit. Thus, when thedevice is activated after being idle for a length of time greater thanthe elapsed time limit, rather than resuming a sleep mode, the devicemay enter the power cut off mode. Thus, the power cut off moduleprevents a cycle of repeated inadvertent activations, which coulddeplete the power in the device's battery.

By implementing a power cut off mode described in this disclosure, atleast the following several advantages accrue: First, a reduction in theeffects of inadvertent activation to avoid depletion of the battery.Second, minimization of the power consumed while a device is off. Third,maintenance of an active real-time clock. The techniques describedherein function to, in part, extend the shelf life of battery-powereddevices such as eBook reader devices and other handheld electronicdevices and enhance a user's overall experience with the device. Thesetechniques may be implemented by an electronic device utilizing aprocessor capable of entering a low power mode. For example, the i.MXarchitecture from Freescale™ Semiconductor Incorporated, of Austin,Tex., United States of America, is one suitable family of processorswith associated power management integrated circuits (PMICs).

The processor executes an operating system, including, but not limitedto, Linux®, UNIX®, Microsoft Corporation's Microsoft Windows®, MicrosoftCorporation's Windows Mobile®, Apple Corporation's Mac OS®, AppleCorporation's Mac OS X®, and Wind River Systems Inc.'s VxWorks®.

For example, an eBook reader device may incorporate a Freescale™processor having an i.MX architecture with an Atlas PMIC and executing aLinux® kernel. The kernel uses device drivers to communicate withperipheral devices such as the PMIC, external memory interfaces (EMIs),Universal Serial Bus (USB) controllers, image processing units (IPUs),and so forth. These peripheral devices may reside on the same “chip” ordie as the processor as in the case of the i.MX architecture and/or mayreside on another die.

While this overview is described in terms of an eBook reader device, theconcepts described herein may also be applicable to cellular telephones,portable media players, desktop computers, laptops, tablet computers,netbooks, personal digital assistants, or other electronic devices.

Illustrative eBook Reader Device

FIG. 1 is an illustrative electronic device 100 such as an eBook readerdevice 102. While this figure illustrates an eBook reader device forexample purposes, other implementations may employ any other type ofelectronic device, as discussed above.

As described in more detail below with regards to FIGS. 2-6, a power cutoff module 104 is configured to place the eBook reader device 102 into apower cut off mode. While in the power cut off mode, the real-time clockremains operational and the device will awaken upon a sustained wakeupinterrupt.

As illustrated, the eBook reader device 102 includes a power switch 106.The power switch 106 and associated circuitry is configured to generatean interrupt upon activation of the switch. In some implementations thepower switch 106 may be a momentary contact switch biased with a springto maintain an open state unless activated, a capacitive switch, and soforth.

The eBook reader device 102 also includes a display 108, as well as akeypad that may include one or more page turning buttons 110 and akeyboard 112 for user input. Furthermore, the keypad may include anyother controls configured to receive user input via buttons, touchscreen inputs, or the like.

FIG. 2 is an illustrative schematic 200 of the eBook reader device 102shown in FIG. 1. A central processor unit (“processor”) 202 is shownwithin eBook reader device 102. Memory 204 within the eBook readerdevice 102 may store an operating system 206 comprising a kernel 208.

The memory 204 may also store the power cut off module 104, which iscoupled to kernel 208. The power cut off module 104 is configured toperform specific acts, including placement of the device into a powercut off mode.

Kernel 208 may operatively couple to one or more device drivers 210 thatare stored in memory 204. These device drivers 210 may include a displaydriver, external memory interface driver, USB host controller driver,and so forth. The device drivers 210 are operatively coupled to devices212. Several illustrative devices in eBook reader device 102 aredescribed next.

FIG. 2 also illustrates that the device 102 may include a powermanagement integrated circuit (PMIC) 214. The PMIC 214 is configured to,among other functions, distribute and control power to the processor202, the devices 212, and so forth. For example, the PMIC 214 may beconfigured to maintain a wait-for-interrupt state. While in thewait-for-interrupt state, upon receiving a wakeup interrupt, the PMIC214 will power up the processor 202 and other devices 212 to a runningawake mode. In some implementations, the PMIC 214 may be specific to aparticular processor 202. For example, where the processor 202 is amember of the Freescale™ i.MX family, a corresponding Atlas family PMICmay be used.

The PMIC 214 may incorporate, or couple to, a real-time clock (RTC) 216.The RTC 216 is configured to maintain a clock suitable for trackingcalendar date and time. The RTC 216 may be used for several purposes,including acting as a source of information for digital rightsmanagement (DRM), providing time comparison for a global position systemunit for ephemeris checking, and so forth.

The RTC 216 may facilitate DRM-controlled interactions. For example, auser of a first eBook reader device may loan an eBook to a second userfor the month of May. The RTC's 216 in each eBook reader device 102 maybe used to enforce that the loaned eBook is inaccessible to the firstuser and accessible to the second user during the month of May. Forexample, when the first user attempts to access the loaned eBook duringthe month of May (as indicated by the RTC 216), the DRM may prohibitaccess to the eBook that has been temporarily loaned to the second userduring this time period.

The RTC 216 may be periodically updated from an external reference, suchas a user input, cellular network time, network time protocol, and soforth. Maintaining the RTC 216 enhances the user experience by allowingDRM functionality even when no external reference is available or whenthe external reference is not deemed to be trustworthy.

In some implementations, the RTC 216 may be coupled to an RTC battery218. The RTC battery 218 may provide a power source independent of aprimary battery within the eBook reader device 102 to maintain operationof the RTC 216. For example, the RTC battery 218 provides power for theRTC 216 to continue functioning when the primary battery is depleted orremoved. The RTC battery 218 may comprise a capacitor, coin cell, and soforth.

An image processing unit 220 is shown coupled to a display 222. Forexample, display 222 may be display 104 on eBook reader device 102described above with reference to FIG. 1. Image processing unit 220 maybe configured to, at the direction of processor 202, take input data andgenerate an image suitable for presentation on a display 222. Forexample, the text data of an eBook may be converted into a bitmap of thepage suitable for presentation on the display 222.

The display 222 may be capable of presenting an image while theprocessor 202 is in a low power or off mode. Reflective displaysincluding electrophoretic displays, cholesteric liquid crystal displays,electrofluidic displays, and so forth present an image without appliedpower. In some implementations, displays that present an image usingapplied power, such as an organic light emitting diode (“OLED”) display,may be configured to enter a self-refresh mode, allowing the display toremain active and present content while the processor 202 is in the lowpower or off mode. In some implementations, the eBook reader device 102may comprise two or more displays using different technologies. Forexample, a first display may comprise an electrophoretic display while asecond display comprises an OLED.

The eBook reader device 102 may also include a keypad 224 coupledthereto. For example, this may be the keypad of eBook reader device 102described above, which incorporates page turn buttons 110 and keyboard112. As described above, the device may also include a power switch 106.Activation of the power switch 106 generates an interrupt that may beused to trigger a change in power state. For example, when the eBookreader device 102 is in a sleep mode, activation of the power switch 106may wakeup the device. In another example, the duration of activation ofthe power switch 106 may be used to specify a particular mode. Forexample, a two-second activation while the device is in awake mode mayresult in the device entering a sleep mode, while a four-secondactivation may place the device in the power cut off mode.

Various sleep or low power modes may be used, including that which isdiscussed in pending U.S. patent application Ser. No. 12/261,980 filedOct. 30, 2008 and entitled “Low Power Mode for Processor.” For example,on the Freescale architecture, the low power modes many include a dozemode or a state retention mode. While in a low power mode, powerconsumption is reduced. This reduction in power consumption may beaccomplished by shutting down unused hardware, reducing supply voltages,and so forth.

When the eBook reader device 102 is in an active awake mode, activationof the power switch 106 may trigger entry into a sleep mode, or a powercut off mode. Configuration, duration of the activation, and so forthmay determine whether sleep or power cut off mode are triggered.

FIG. 2 illustrates that the device may further include an ExternalMemory Interface (“EMI”) 226. EMI 226 may be coupled to external memory228, which may comprise Static Random Access Memory (“SRAM”),Pseudostatic Random Access Memory (“PSRAM”), Synchronous Dynamic RandomAccess Memory (“SDRAM”), Double Data Rate SDRAM (“DDR”), NAND Flash, andso forth. In some implementations, at least a portion of the power cutoff module 104, operating system 206, applications, content, and soforth, may be stored in the external memory 228.

The device may also include a USB controller device 230, which maycouple to USB devices 232, such as a wireless wide area network modem.The USB controller device 230 may comply with any of the USB standardsincluding USB 1.0, 1.1, 2.0, 3.0 as set forth by the USB ImplementersForum.

The device 102 may also include a hard drive 234, which may use magneticor optical memory on spinning disks or solid state storage. The harddrive 234 may be used to store content for consumption by the user, suchas electronic books.

The eBook reader device 102 may further include one or more otherdevices. These other devices may include a Firewire bus, camera, globalpositioning system receiver, Bluetooth™ wireless device, PC Card device,and so forth.

Operative couplings, such as those between the kernel 208, the power cutoff module 104, and the device drivers 210 are shown for emphasis. Alldevices in FIG. 2 are operatively coupled, with their respective arrowsomitted only for clarity of illustration.

Illustrative Processes for Power Cut off Mode

FIG. 3 is an illustrative process 300 that an electronic device 100,such as an eBook reader device 102, may implement using a power cut offmodule 104. This process may help prevent inadvertent activations, mayminimize power consumption of the device while the device is off, maymaintain a real-time clock, and so forth.

Operation 302 shows an eBook reader device 102 in a power cut off mode304. In the power cut off mode 304, power is discontinued to componentswithin the eBook reader device except for portions of the PMIC 214, suchas the RTC 216 and wait-for-interrupt circuitry. For example, theprocessor 202, the memory 204, the display 222, the hard drive 234, theexternal memory 228, the USB devices 232, the devices 212, and so forthare off while the device remains in the power cut off mode 304.

Operation 306 shows the eBook reader device 102 receiving a transientwakeup interrupt while in power cut off mode 304. This transient wakeupinterrupt may include a momentary activation of the power switch. Insome implementations, the transient wakeup interrupt comprises aduration of less than 25 milliseconds. In contrast, a sustained wakeupinterrupt comprises a duration of at least 25 milliseconds. In someimplementations, the duration of the transient wakeup interrupt maycomprise a duration of less than 100 ms, while a sustained wakeupinterrupt comprises a duration of at least 100 ms.

Transient wakeup interrupts may be generated by factors that areexternal or internal to the eBook reader device 102. For example, asshown here at operation 306 the eBook reader device 102 may be jostledor bumped, resulting in the power switch 106 being physically bouncedand generating a transient wakeup interrupt. This jostling may occurduring shipment of the device, during travel by the user, and so forth.Other inadvertent transient activations may occur as a result of thepower switch 106 brushing other objects. For example, the user placingthe eBook reader device 102 in a backpack filled with other items mayresult in a transient wakeup interrupt.

Operation 308 shows the device remaining in power cut off mode. Here,the power cut off module 104 has disregarded the transient wakeupinterrupt resulting from the jolt, due to the fact that the duration ofthe transient wakeup interrupt was below a pre-determined threshold. Asa result, the battery of the device 102 has not been needlessly depletedby an unnecessary and, here, unintended awakening.

Operation 310 shows the user pressing and holding the power switch forat least a pre-determined period of time. When this period exceeds thepre-determined threshold, a sustained wakeup interrupt is generated.

Operation 312 shows the PMIC 214 receiving the sustained wakeupinterrupt. The wait-for-interrupt circuitry, which has been minimallyactive, is triggered by the sustained wakeup interrupt and begins thepower up of the PMIC 214. The PMIC 214 powers up the regulators, whichprovide power to components of the device 102. Once power is applied tothe processor 202, memory 204, device 212, and so forth, the restart ofthe device begins. The device is now in an awake mode 314, with thecomponents of the device 102 being active and operational.

FIGS. 4-6 illustrate example processes 400, 500, and 600 that may beimplemented by the architecture of FIGS. 1-2 or by other architectures.These processes are illustrated as a collection of blocks in a logicalflow graph, which represent a sequence of operations that can beimplemented in hardware, software, or a combination thereof. In thecontext of software, the blocks represent computer-executableinstructions stored on one or more computer-readable storage media that,when executed by one or more processors, perform the recited operations.Generally, computer-executable instructions include routines, programs,objects, components, data structures, and the like that performparticular functions or implement particular abstract data types. Theorder in which the operations are described is not intended to beconstrued as a limitation, and any number of the described blocks can becombined in any order or in parallel to implement the processes.

FIG. 4 is an illustrative flow diagram of a process 400 for awakening adevice from a sleep mode and entering a power cut off mode. A device maybe configured to transition from an active awake mode to a sleep modeafter a given period of inactivity or in response to a particular input.For example, the eBook reader device 102 may be configured to enter alow-power sleep mode after ten minutes of no input, after receiving amomentary activation of the power switch 106, and so forth.

Once in the low power sleep mode, the device may be inadvertentlyactivated. For example, as described above the device may be jostled,resulting in a transient wakeup interrupt. It is worthwhile to avoid orminimize a cycle of inadvertent wakeups which could lead to depletion ofthe battery.

At 402, an eBook reader device 102 is in sleep mode. While sleep modeaffords a significant reduction in power consumption over that requiredduring awake mode operation, power usage as indicated by graph 404continues. For example, in some implementations the sleep mode mayconsume about 0.400 milliamps (mA). Over the course of several months,such as during shipment, warehousing, transport to the customer, and soforth, even this low power draw may deplete the battery. As a result ofthis depletion, the user activating the device for the first time may befaced with a lengthy and discouraging charging interval to replenish thedepleted battery.

At 406, the device receives a wakeup interrupt and resumes an awakemode. Once awake, at 408 when the device determines one or morepre-determined conditions have been met, the process may proceed to 410.

An administrator, programmer, application, or the user may specify oneor more of the pre-determined conditions and associated threshold valuesupon which the device will engage the power cut off mode.

The pre-determined condition may comprise an elapsed time limit sincelast action by a user. In this implementation, when the device has beenunused for a pre-determined amount of time the device will engage thepower cut off mode. The power cut off module calculates an elapsed timeby accessing a last active time comprising the date and time of a lastaction by the user, such as stored in a system log file. The time lastactive may be the last time of a user input, last access of contentstored on the device, and so forth. A current time is accessed from theRTC 216 which has remained operational and thus provides accurate dateand time. An elapsed time since last active is calculated by subtractingthe current time from the time last active. The elapsed time since lastactive is compared with an elapsed time limit. When the elapsed timesince last active exceeds a pre-determined threshold value, the processmay proceed to 410. Otherwise, the pre-determined condition(s) are notmet in this example and the device remains awake.

In another implementation, the pre-determined condition may comprise acurrent battery status. For example, when the battery status drops belowa threshold value, the device may engage the power cut off mode.

In yet another implementation, the pre-determined condition may be aflag indicating when the device has completed initial setup by the user.A device in transit which has not yet been used or personalized throughthe initial setup by the user would thus have the flag set to a valueindicating this un-configured state. Thus, when the device has not beensetup by the user, the process may proceed to 410.

When, at 408, the one or more pre-determined conditions are met, at 410the power cut off mode is engaged. As described below in more detailwith regards to FIG. 5, the power cut off mode shuts down the operatingsystem and deactivates power to each component of the device 102 exceptthe RTC 216 and wait-for-interrupt circuitry.

While in the power cut off mode, power consumption of the device issignificantly reduced as compared to the sleep mode, as shown by graph412. For example, power consumption may be decreased while in power cutoff mode to about 0.034 mA, or about 8.5% of the power used in sleepmode. This decrease in power consumption results in a correspondingincrease in the period of time during which the device may be storedwithout depleting the battery. For example, rather than a few months ofstorage possible with the device in sleep mode, the device in power cutoff mode may be stored for years before depleting the battery.

FIG. 5 is an illustrative flow diagram of a process 500 for engaging apower cut off mode. While the following flow diagram is described usingterms, applications, and command present within the Linux operatingsystem, it is understood that this process may also be applied to otheroperating systems. Furthermore, the following process is described forillustration, and not by way of limitation, as executing on the i.MXarchitecture using an Atlas PMIC, such as an Atlas Light, chip modelnumber MC13892.

At 502, a userspace application executes a halt or reboot program. As apart of the halt, the init program is run with argument 0, which sends ashutdown signal to all running processes.

At 504, the processes on the device are shutdown at least partly inresponse to receiving the shutdown signal. Once the userspaceapplications have shut down, control is transferred to the operatingsystem kernel 208.

At 506, the operating system kernel 208 sends a shutdown event to eachregistered device driver 210 of the device. The device drivers 210 inturn shutdown or stop associated devices 212. After each of the devices212 have been stopped, control is transferred to a core kernel code,which handles the shutdown or otherwise places the device into OFF mode.

At 508, the PMIC 214 is configured for power cut off mode. A wakeupsource is configured, and the RTC 216 is configured to remain active.Each switching and linear regulator is also configured to be turned off.For example, this includes the switching regulators SW1, SW2—CPU Core,SW4—DDR, and so forth.

Because a restart of the device is not desired in some instances, awatchdog reset signal WDIRESET is configured to 0, which prevents arestart. For example, this may involve setting a RESTARTEN bit to “0” inAtlas register 15.

A universal serial bus input voltage (VUSBIN) may also be turned offwhen the device is not operating in USB On-The-Go mode. When on, theSWBST is internally switched to supply the VUSB regulator, and SWBSTwill drive VBUS from the VUSBIN pin. This results in a leakage currentof about 0.150 mA, resulting in unnecessary power consumption.

The PMIC 214 configuration also includes configuring the watchdog resetsignal (WDIRESET) pin on the power management integrated circuit as ageneral purpose input/output interface (GPIO). The WDIRESET pin is usedin the next step to finalize the power cut off mode.

At 510, the PMIC 214 is placed into the power cut off mode. The placingof the PMIC 214 into the power cut off mode comprises setting thewatchdog reset signal pin to a logical low voltage value, which in turnplaces the PMIC 214 into OFF mode. While in this off mode, the PMIC 214retains the operation of the RTC 216 and the wait-for-interruptcircuitry. Because the RESTARTEN bit has been cleared, the Atlas doesnot restart, which would in turn lead to a reset on the processor 202.The device now settles into the power cut off mode.

FIG. 6 is an illustrative flow diagram of a process 600 for restarting adevice in the power cut off mode. At 602, a sustained wakeup interruptis received. Depending upon configuration, the sustained wakeupinterrupt is a wakeup interrupt having duration of at least 25milliseconds. By requiring a sustained wakeup interrupt, inadvertentactivations are minimized or eliminated altogether.

At 604, the PMIC 214 is awakened and the switching and linear regulatorsare powered up, thus bringing the device into the awake mode. At 606,the device begins the restart, with the processor 202 loading andexecuting the operating system 206 and other applications.

CONCLUSION

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described. Rather,the specific features and acts are disclosed as illustrative forms ofimplementing the claims. For example, the methodological acts need notbe performed in the order or combinations described herein, and may beperformed in any combination of one or more acts.

What is claimed is:
 1. A method comprising: pausing operation of anelectronic device; terminating one or more processes running on theelectronic device; sending a signal to stop operation of one or morecomponents of the electronic; designating a source for a wakeup signal;configuring a power management integrated circuit of the electronicdevice for a power cut off mode, wherein the configuring the powermanagement integrated circuit includes configuring a reset signal pin onthe power management integrated circuit as an input/output interface,and wherein, in the power cut off mode, wait-for-interrupt circuitry inthe power management integrated circuit is operational; and setting areal-time clock to remain active with the power management integratedcircuit in the power cut off mode.
 2. The method as recited in claim 1,further comprising, prior to the activating, configuring the electronicdevice for the power cut off mode by setting at least one powerregulator to transition to an off state to power down a centralprocessor unit of the electronic device when the power cut of mode isactivated.
 3. The method as recited in claim 2, wherein setting the atleast one power regulator comprises setting at least one of a switchingregulator or a linear regulator in a power management integrated circuitto transition to the off state, the configuring the electronic devicefor the power cut off mode further comprising: clearing a restartregister bit in the power management integrated circuit to prevent arestart; and turning off a universal serial bus input voltage, whereinthe reset signal pin is configured to place the power managementintegrated circuit into the power cut off mode when set to a lowvoltage.
 4. The method as recited in claim 1, further comprising:receiving a wakeup signal while the electronic device is in the powercut off mode; and at least partially in response to the wakeup signalbeing received for a duration less than a threshold duration,maintaining the power cut off mode.
 5. The method as recited in claim 1,further comprising: receiving a wakeup signal while the electronicdevice is in the power cut off mode; and at least partially in responseto the wakeup signal being received for a duration that exceeds athreshold duration, causing powering up of at least a portion of theelectronic device.
 6. The method as recited in claim 5, wherein causingpowering up of at least the portion of the electronic device comprisescausing activation of at least one power regulator to power up a centralprocessor unit of the electronic device.
 7. The method as recited inclaim 1, further comprising activating the power cut off mode inresponse, at least in part, to at least one of: determining that athreshold amount of time has elapsed since a user action; determiningthat a current battery status is below a threshold value; or determiningthat the electronic device has not completed an initial setup.
 8. Anelectronic device comprising: a central processor unit; a non-transitorycomputer-readable medium coupled to the central processor unit; areal-time clock; and a power cut off module, maintained in thecomputer-readable medium and configured to be executed by the centralprocessor unit to: designate a source for a wakeup signal; set thereal-time clock to remain active; retain operation of await-for-interrupt circuitry; and activate a power cut off mode for theelectronic device, wherein the power cut off mode comprises poweringdown the central processor unit and, in the power cut off mode, powerconsumption of the electronic device is no more than about 0.034 mA. 9.The electronic device as recited in claim 8, wherein the power cut offmodule is further configured to be executed by the central processorunit to: pause operation of the electronic device; terminate one or moreprocesses running on the electronic device; and send a signal to stopoperation of one or more components in the electronic device.
 10. Theelectronic device as recited in claim 8, further comprising a powerswitch as the source for the wakeup signal.
 11. The electronic device asrecited in claim 8, wherein the power cut off module is furtherconfigured to be executed by the central processor unit to: set at leastone of a switching regulator or a linear regulator in a power managementintegrated circuit to transition to an off state in response toactivation of the power cut off mode; clear a restart register bit inthe power management integrated circuit; turn off a universal serial businput voltage; and configure a reset signal pin on the power managementintegrated circuit as a input/output interface, the reset signal pinconfigured to place the power management integrated circuit into thepower cut off mode when set to a low voltage.
 12. The electronic deviceas recited in claim 8, wherein the power cut off module is furtherconfigured to be executed by the central processor unit to activate thepower cut off mode at least partly in response to determining that acondition has been met, the power cut off mode configuring theelectronic device to await a sustained wakeup signal before powering upthe electronic device from the power cut off mode.
 13. The electronicdevice as recited in claim 12, wherein the power cut off module isfurther configured to be executed by the central processor unit todetermine that the condition has been met based at least in part on atleast one of: determining that a threshold amount of time has elapsedsince a user action; determining that a current battery status is belowa threshold value; or determining that the electronic device has notcompleted an initial setup.
 14. The electronic device as recited inclaim 12, wherein the sustained wakeup signal comprises a wakeup signalhaving a duration of at least 25 milliseconds.
 15. A method comprising:receiving, at an electronic device, a wakeup signal while the electronicdevice is in a power cut off mode, wherein, in the power cut off mode, acircuit of the electronic device is configured to receive a wakeupsignal; a central processor unit, switching regulators, and linearregulators of the electronic device are powered down; and a powermanagement integrated circuit of the electronic device retains theoperation of a real time clock and wait-for-interrupt circuitry; andbased at least in part on a duration of the wakeup signal exceeding athreshold duration, the circuit causing at least a portion of theelectronic device to power up from the power cut off mode.
 16. Themethod as recited in claim 15, further comprising, prior to receivingthe wakeup signal: pausing operation of an electronic device;terminating one or more processes running on the electronic device;sending a signal to stop operation of one or more components of theelectronic device; designating a source for a wakeup signal; setting areal-time clock to remain active; and activating the power cut off modefor the electronic device to power down the central processor unit. 17.The method as recited in claim 15, further comprising, prior to theactivating, configuring the electronic device for the power cut off modeby: setting at least one power regulator to transition to an off stateto power down the central processor unit of the electronic device; andconfiguring the circuit to maintain the power cut off mode until receiptof the wakeup signal exceeding the threshold duration.
 18. The method asrecited in claim 15, wherein causing at least a portion of theelectronic device to power up from the power cut off mode comprisescausing activation of at least one power regulator to supply power tothe central processor unit to enable booting of an operating system. 19.The method as recited in claim 15, wherein exceeding the thresholdduration comprises receiving the wakeup signal for at least 25milliseconds.
 20. The method as recited in claim 15, further comprising:prior to receiving the wake up signal, receiving another wake up signalwhile the electronic device is in the power cut off mode; and based atleast in part on a duration of the other wakeup signal being less thanthe threshold duration, the circuit causing the electronic device tomaintain the power cut off mode.